The Lib Dems have started a campaign about the US/UK lopsided extradition treaty. Essentially the US can extradite a UK citizen without presenting probable cause. For the innocent, this can mean a multiple year trial (as well as expensive defence) in the US.
In the case of the Natwest Three, as I understand it the alleged crime would have taken place in the UK, by UK citizens against UK interests. The employers (who are the alleged victims) have not wished to press any charges. As there is a loose connection to Enron, the US want to press charges but have not presented a probable cause to the UK. If the UK want to extradite a US citizen then the same arrangements do not apply. A special relationship indeed.

This treaty was originally presented as a bill which would aide the extradition of terror suspects (also without probable cause, but in these days the concept of evidence seems secondary when we have terror suspects) - and yet it's scope is wider than was originally spun. This is a good case in point why legislation should be tightly drawn and why 'trust us' isn't enough.

I suppose that this is the special part of the special relationship that we keep hearing about?

Here are the other articles which Boris wrote, (I knew the Boris Plugin for Firefox would be handy!) from May 2005 and July 3rd 2006. This isn't the only case out there, there are others. My issue is not that I think there's no case to answer, I don't have anything like the information needed to make a judgement - and have no opinion on the individual cases.